Numerous efforts have been made in the past to develope controlled release pesticides. One approach has been to coat particles of an insecticide with a polymeric coating, for examples, as described in U.S. Pat. No. 3,569,769 or U.S. Pat. No. 3,269,900. Another approach has been to chemically couple the pesticide directly to a natural polymeric substance, such as bark, as described in Canadian Pat. No. 863,310. Still another approach has been to use a bridging compound to chemically connect the pesticide to a natural polymeric substrate as described in Canadian Pat. No. 855,181. Pesticides also have been dissolved in waxes, incorporated in emulsions and combined with large amounts of inert carriers in efforts to obtain controlled release compositions.
None of the described approaches has been completely successful. Coating particles of a pesticide with a polymer film is a relatively expensive process; the use of natural polymer substrates, such as bark, can result in a product which is of non-uniform consistency from batch to batch and bulky to handle and transport, and the incorporation of a pesticide into emulsions, waxes and compositions including inert carriers can result in compositions which do not provide for an even controlled release of the active pesticide.